2017 was the year of high profile data breaches and ransomware attacks, but from the beginning of this year, we are noticing a faster-paced shift in the cyber threat landscape, as cryptocurrency-related malware is becoming a popular and profitable choice of cyber criminals.

Several cybersecurity firms are reporting of new cryptocurrency mining viruses that are being spread using EternalBlue—the same NSA exploit that was leaked by the hacking group Shadow Brokers and responsible for the devastating widespread ransomware threat WannaCry.

Active since at least May 2017, Smominru botnet has already infected more than 526,000 Windows computers, most of which are believed to be servers running unpatched versions of Windows, according to the researchers.

"Based on the hash power associated with the Monero payment address for this operation, it appeared that this botnet was likely twice the size of Adylkuzz," the researchers said.

The botnet operators have already mined approximately 8,900 Monero, valued at up to $3.6 million, at the rate of roughly 24 Monero per day ($8,500) by stealing computing resources of millions of systems.

The highest number of Smominru infection has been observed in Russia, India, and Taiwan, the researchers said.

The command and control infrastructure of Smominru botnet is hosted on DDoS protection service SharkTech, which was notified of the abuse but the firm reportedly ignored the abuse notifications.

According to the Proofpoint researchers, cybercriminals are using at least 25 machines to scan the internet to find vulnerable Windows computers and also using leaked NSA's RDP protocol exploit, EsteemAudit (CVE-2017-0176), for infection.

"As Bitcoin has become prohibitively resource-intensive to mine outside of dedicated mining farms, interest in Monero has increased dramatically. While Monero can no longer be mined effectively on desktop computers, a distributed botnet like that described here can prove quite lucrative for its operators," the researchers concluded.

"The operators of this botnet are persistent, use all available exploits to expand their botnet, and have found multiple ways to recover after sinkhole operations. Given the significant profits available to the botnet operators and the resilience of the botnet and its infrastructure, we expect these activities to continue, along with their potential impacts on infected nodes."

Since it does not download any application to an infected computer, WannaMine infections are harder to detect by antivirus programs. CrowdStrike researchers observed the malware has rendered "some companies unable to operate for days and weeks at a time."

Since recently observed cryptocurrency mining malware attacks have been found leveraging EternalBlue, which had already been patched by Microsoft last year, users are advised to keep their systems and software updated to avoid being a victim of such threats.